The present invention relates to a semiconductor integrated circuit device and, more particularly, to a semiconductor integrated circuit device for driving a vacuum fluorescent display device (hereafter referred to as a "VFD"). The vacuum fluorescent display device is constructed basically of:
(1) an anode made of a fluorescent material;
(2) a cathode for emitting electrons; and
(3) a grid interposed between the anode and the cathode for controlling the migration of the electrons.
When the cathode is supplied with a specified voltage, it is heated to about 650.degree. C. to emit the electrons. If a positive voltage is applied to both the (fluorescent) anode and the grid, the electrons emitted from the cathode pass over the grid and are accelerated to impinge upon the fluorescent material, whereupon this material emits light. The vacuum fluorescent display device, in which fluorescent dots are arrayed in a matrix shape, is called a "dot matrix vacuum fluorescent display device".
In recent years, he need has increased for producing graphic fluorescent display panels having extremely high display capacity and density. In view of this technical trend, we have investigated developments of dot matrix displays of capacity as high as 240 dots (vertically).times.320 dots (horizontally) or fluorescent display tubes and have revealed the following functions required for the drive IC of a vacuum fluorescent display device:
(1) In order to achieve high luminosity of a fluorescent display tube, it is necessary to abruptly accelerate the electrons generated from the cathode and to make them impinge upon the fluorescent material at high speed. In order to attain high luminosity, a voltage as high as 250 V has to be applied to the anode and the grid. Therefore, the drive device (or the driver IC) for the anode and the grid must be able to withstand a considerably high voltage.
(2) In order to improve the display function of the fluorescent display tube of high capacity, moreover, it is necessary to scan (or drive) the fluorescent matrix at a high speed. For this reason, it is necessary to remarkably shorten the period from the time when data is input to the time when the drive output is generated. This makes it necessary to operate the anode and grid driver at high speed.
(3) In order to reduce heat dissipation of the driver IC, this IC has to be operated with low power consumption.
(4) In order to reduce the size of the vacuum fluorescent display device, the chip area of the driver IC has to be made small.
In order to satisfy the needs for the high luminoscity and capacity of the fluorescent display tube, as has been described above, the anode and grid driver are required to have a high voltage function, high speed, low power consumption and must be small. It is, however, very difficult to satisfy all those requirements. Therefore, it is difficult to integrate the driver.
These difficulties will be described in the following from the respective standpoints of the circuit, device and layout.